1. Field of the Invention
The present invention relates to a method of establishing communication between a terminal coupled to an Internet Protocol (IP) network and a terminal coupled (via Point-to-Point Protocol (PPP) to a remote access server. More particularly, the present invention relates to a communication protocol between a gatekeeper and a remote access server.
2. Description of the Related Art
FIG. 1 illustrates a simplified network structure diagram for enabling the terminal C 12 connected to a Public Switched Telephone Network (PSTN) or Integrated Service Digital Network (ISDN) 10 to access the IP network by performing a dial-up connection to a remote access server 20. In this case, the terminal C 12 makes a direct point-to-point (PPP) connection to the remote access server 20 that is assigned to an IP address, so that the terminal 12 can exchange packet data with a particular host through the IP network 30.
FIG. 2 is a simplified network structure as recommended by International Telecommunication Union-Telecommunication (ITU-T) Standardization Sector, namely, Packet-based Multimedia Communications System, H.323. The H.323 provides a standard for enabling the H.323 terminals to make multimedia communication with each other in a packet-based network, such as IP network, which includes a gatekeeper 38, terminals 32 and 36, a gateway 34, and a Multipoint Control Unit (MCU)(not shown). The communication protocol between these entities is provided to perform network specific protocol functions. According to the communication protocol, the terminals should register their aliases and IP addresses in the gatekeeper 38 and receive admission from the gatekeeper 38 to communicate with each other. To this end, specific protocol functions, such as the Registration, Admission, Status (RAS), and the Q.931 signaling of ITU-T Line Transmission of Non-Telephone Signals H.225.0 are performed.
FIG. 3 is a flow diagram illustrating the process of exchanging messages to enable the terminal A to make a connection to the terminal B of FIG. 2 in a H.323 communication compliant network. Firstly, both the terminals A and B send Registration Request (RRQ) messages to a gatekeeper to register their aliases (or telephone number) and IP addresses in steps 50-1 and 50-3, and in turn receive Registration Confirm (RCF) messages from the gatekeeper in steps 50-2 and 50-4. Secondly, the terminals are enabled to communicate with each other using the aliases and IP addresses information retrieved from the gatekeeper. In response to retrieving the IP address information of the receiving terminal, the sending terminal A exchanges an Admission Request (ARQ) message and an Admission Confirm (ACF) message with the gatekeeper, in steps 50-5 and 50-6, in order to receive the admission for communication. Upon receiving the ACF message from the gatekeeper, the sending terminal A sends the Q.931 setup message for call signaling to the receiving terminal B in step 50-7, as shown in FIG. 3. Then, the receiving terminal B in turn exchanges the ARQ message and the ACF message with the gatekeeper, in steps 50-8 and 50-9, in order to receive the admission for communication. Upon receiving the ACF message from the gatekeeper, the receiving terminal B sends the Q.931 connection message to the sending terminal A in step 50-10, then the terminal A performs the H.245 call signaling to establish communication with the terminal B in step 50-11.
FIG. 4 illustrates a simplified structure of the combined networks in FIGS. 1 and 2. In such an environment, exchanging messages between the terminals is performed by accessing the remote access server 20 by the terminal C 12 to communicate with a specific H.232 terminal, such as terminal A 32 or B 36 connected to the IP network 30. To this end, the terminal C 12 connected to the IP network 30 should register its alias and IP address in the gatekeeper 38 and receive the admission for communication. Thus, if the terminal C 12 maintains a dial-up connection with the remote access server 20, the terminals coupled to the IP network 30 may communicate with the terminal C 12 at any time thereafter. However, when the terminal C 12 does not require communication with the terminals of the IP network 30, the terminal c 12 usually maintains an off-line connection with the remote access server 20 to save the dial-up modem connection charge. If the dial-up connection with the remote access server 20 is terminated, the terminal C 12 loses its IP address and its registered information in the gatekeeper 38. As a result, the terminals coupled to the IP network can not establish communication with the terminal C connected to a circuit network, such as PSTN or ISDN.